Some serious expert advice please.
I know some users here are quite expert in their field as I have read a number of topics posted here.

2009 Golf piston - 28000Klms on clock. BTW this is only a very recent problem.

Can you tell from these piston pic's (same piston) if the damage was caused by:
1. Fuel
2. Oil
3. Faulty part

In time I will be able to put up the whole story but for now I would like to see whos experience is up for the challenge.

I say pre-ignition or heavy detonation, AF being to lean or over advanced timing. wait? this is a new car!

Air leak in manifold? cheap crap fuel with low octane?


Hard to tell from those pics, to me it looks melted.

but at the same time sort of looks like its broken, so if thats the case, high milage granny driven engine then suddenly thrashed causing the rings to interfere with the wear ridge on the cylinder wall?

looks brittle

oil.....

Hmm, but heavy detonation usually either turns the piston tops into swiss cheese with craters or eats away the big end bearing due to the load as the piston is pushed up. My toyota piston didn't break in two until the bearing got that worn it made contact with the head and busted in two as a result of lean running on cylinder 3 (clean piston top, hot looking colour on spark plug. Thats what the post-mortum concluded with after a few observations.

What does the piston top look like? what colour?

btw i'm no qualified expert (still studying but in last year). Don't know if this helps: "Impacted specimens with small fracture energy or with a very little plastic deformation is said to be in a brittle manner whereas fracture of a metal after extensive plastic deformation is said to be in a ductile manner. Brittle fracture looks clear and shinny, while ductile fracture appears grayish and fibrous. This post-fracture visual surface analysis can provide information on the degree of ductility/brittleness of the material ding impact."

The fracture doesn't appear to be brittle but moreso ductile. Could very well be a defective part. If it was brittle it would have alot of crystalline structures and be more a clean break. The fibres are your instant hint of ductility there. Mind you hot running would make it more ductile than brittle anyways (without going into work hardening which occurs over time)

Usually quality control allows for a certain around of crack length before it is classed as defective with the potential risk of premature failure. It can be seeded in the piston all the way back to how it was moulded and/or heat treated in regards to the alignment of the metal grain boundaries. Under enough load, the crack will slowly propagate and accelerate as the length is increased over time until the part completely fails.

Hows the big end bearing look?

I'd say It's a faulty flux regulator
resulted in the system triying to go back to the future
before the flux capacitor is charged to atleast 1.21 Gigawatts
which caused the flux dispersal to loop back and this energy had to go somewhere so
release pseudo-randomly in to the environment which
just happen to be the ring groove lip.
thus the temporal displacement caused the thing to break
because it tried to occupy two space at one time
ie being in two place at once.

Do you run Optimax (or what ever its called now)?

hmmmmm defective part...

that looks like a faulty casting or forging
as theres no damage to the top only the side of the piston on the ring lands

To me it looks like the cracked area goes out each side from the hole for the pin for the lower ring. The pin that would stop the ring from being able to turn. The lower ring would be the oil control ring. Or maybe the crack has stopped at the hole.

It does look to me like the problem has located itself in the area of the pin hole. Has the pin come loose? Has the assembly been done wrong, causing a problem with the pin hole. Pin or hole was damaged on assembly.

Could have been cause by a number of things.
To much boost too if turbo engine can cause ring lands to fail.
Could be too much compression wrong head gasket if engine has been apart.
Water in cylinder leaky head gasket cauing increase in compression streesing ring lands
Wrong fuel or poor fuel quality will cause knocking and can result in this as well.

Since there is not much scoring on the piston skirt i doubt oil has anything to do with the failure.
Is the vehicle in question petrol or diesel turbo any other work done prior to finding this.
At this stage i will say fuel as the cause.

Could also be caused by gummed up rings, expanding and breaking the ring lands.

inclusion possibly (hair line crack) faulty part, hmmmn, thats my guess.

paul

What model is the Golf?

118TSI twin charged?

If so, this is a very common failure!!!!!

This is a very very common problem with the 118 tsi cavd engine code ill give you a quick run down why this happens. I have replaced aleast 20 engines when working for vw let alone all the others that have been done. The problem well what the factory was telling us is the engines were running to lean causing the ring land to brake apart which then causes a misfire due to loss of compression the problem dosent happen as much anymore due to a software upgrade recall (24S4) its not the biggest deal you will have a brand new engine fitted with the newest software uploaded to your car and should be as good as gold.

Yes, its a 118TSI engine.

Thank you for all your input.

I went with oil as the cause as the pistons I have seen that are damaged by detination look vastly different to what these did.

"motha" and "Sick68VW" explanation was correct and is what the VW dealer went with here. A new motor and software upgrade (even though it had all its previous software upgrades) and it been back on the road for a month. So far so good.